Solution in which gas is dissolved is used for various kinds of application. If exemplifying carbon dioxide gas as a gas, weak carbonic water having a low carbon dioxide gas concentration, carbonic beverage whose carbon dioxide gas concentration is intensified under a high pressure, artificial carbonated spring in which carbon dioxide gas is dissolved in hot water, carbon dioxide dissolved solution used for industrial purpose and the like have been widely used.
Generally, hot spring effects such as blood vessel expansion effect gained in taking bath in hot water containing carbon dioxide gas such as carbonated spring and difficulty of chilling after bath have been well known and utilized in public springs and the like using hot spring since before. The keeping warm effect of the carbonated spring is, basically, considered to be because the physical environment is improved by distal blood vessel expansion effect of contained carbon dioxide gas. Further, carbon dioxide enters the skin so that capillary beds are increased and expanded thereby improving circulation of blood in the skin. Thus, it is considered that this has an effect in cure on regressive disease and distal circulation trouble. Further, a curative effect under a high concentration of about several hundreds mg/l to 1,000 mg/l has been verified in recent years. For the reasons, chemicals and devices capable of providing carbonic water for bath easily have been marketed.
To obtain such carbonated spring artificially, a chemical method for allowing carbonate to react with acid, a method by using combustion gas from a boiler, a device for blowing carbon dioxide gas directly into a pipe having a throttle as disclosed in Japanese Patent Application Laid-Open NO. 5-238928, a method by using a static mixer as a carbon gas dissolver as disclosed in Japanese Patent Application Publication Nos. 7-114790 and 7-114791, and the like are available.
Recently, many methods for producing carbonated spring by using a membrane have been proposed. For example, Japanese Patent No. 2810694 uses a hollow yarn membrane module incorporating plural porous hollow yarn membranes whose both ends are open and further, Japanese Patent Nos. 3048499 and 3048501, Japanese Patent Application Laid-Open No. 2001-293344 and the like have proposed methods of using a nonporous hollow yarn membrane as a hollow yarn membrane.
As a method for producing carbonated spring using a membrane, a so-called one-pass type in which carbonated spring is produced by passing raw water through a carbon dioxide gas dissolver having a membrane module once and a so-called circulation type in which hot water is circulated in a bath through a carbon dioxide gas dissolver using a circulation pump are available.
Meanwhile, the method by using the porous hollow yarn membrane has such a fear that the membrane turns hydrophilic due to a long term usage so that water leaks to the gas side to seal the membrane surface, thereby initial carbon dioxide gas adding ability is eliminated. Contrary to this, if the nonporous hollow yarn membrane is used, the nonporous membrane exists between the gas side and the liquid side, so that no water may leak to the gas side despite a long term usage. However, there is a fear that because water vapor which is water molecular passes, the passing water vapor is condensed on the gas side, thereby the condensed water (drain) seals the membrane surface.
Thus, according to the Japanese Patent Application Laid-Open Nos. 7-313855 and 7-328403, a drain release valve is disposed on the gas side and the valve is opened/closed periodically to discharge drain from the gas side. However, according to this method, the drain release needs to be carried out frequently for a membrane in which the amount of passing vapor is large and thus, carbon dioxide gas charged on the gas side needs to be discharged into the atmosphere, and therefore, the amount of consumption of carbon dioxide gas is likely to be increased.
On the other hand, if the carbonated spring is produced according to the method by using the membrane, there is a disadvantage that the same carbon concentration cannot be secured each time although the carbonated spring having a high concentration can be obtained most highly effectively. Particularly, if the carbonated spring is produced a number of times continuously on the same day, a phenomenon that the carbonic acid concentration drops in the initial period of carbon dioxide gas passage occurs.
According to the above-described methods, although flow rate and pressure are indicated for control of carbon dioxide gas, only the flow rate is controlled under the pressure control using a pressure control valve or the like which is used by being directly connected to a gas cylinder as indicated in many of the embodiments. Thus, the flow rate of the carbon dioxide gas passing through the membrane differs between the initial period of the passage and its stabilizing period. The reason why the flow rate of the carbon dioxide gas changes is considered to be that because the membrane is cooler than the water temperature in the initial period and the concentration of carbon dioxide gas in the membrane is low, the carbon dioxide is unlikely to pass through the membrane even under the same pressure. However, if carbonated spring having some appropriate concentration is produced, there is no any problem at that time and not so much attention is paid to the accuracy.
However, in case of carbonated spring in the vicinity of a carbon dioxide gas saturated concentration at 40° C., which is around 1200 mg/l, it has been made evident that in terms of its curative effect, a further remarkable effect can be expected and there is no way but changing a though that everything is satisfied if carbonated spring having an appropriate concentration is produced. Thus, a necessity of producing the carbonated spring with a high concentration and excellent reproducibility is generated. On the other hand, the above-mentioned carbon dioxide gas dissolver has been modified frequently so that improvement of carbon dioxide gas dissolving efficiency has been tried gradually. However, a further improvement in the dissolving efficiency has been demanded. Particularly in a full-body bathing device which uses a large amount of carbon dioxide gas, the improvement in the dissolving efficiency is important.
Even a method using pressure control is capable of producing carbonated spring having a high concentration if an operation method by providing with an allowance is used, for example, by setting a slightly excessively high pressure or increasing the operation time in case of a circulation type. However, if such a method is applied, carbon dioxide gas is consumed wastefully, which is not preferable.
Further, in case of application for hospitals, a method of producing high-concentration carbonated spring in as short a time as possible has been demanded in order to care as many patients as possible. However, the circulation type has such a disadvantage that the time for producing the high-concentration carbonated spring is prolonged because no sufficient flow rate is secured in the initial period.
On the other hand, the method for producing carbonated spring with an excellent reproducibility by using the one-pass type has been described in Japanese Patent Application Laid-Open No. 10-277121. According to this method, the concentration of carbon dioxide gas in the produced carbonated spring is measured and by feeding back the concentration, the quantity of carbon dioxide gas supplied is controlled. For the reason, it takes a long time to reach a target carbon dioxide gas concentration. Further, this method has such a disadvantage that if alkali degree of raw water changes, no excellent reproduction can be attained.
Examples of the method for measuring the concentration of gas in a gas dissolved solution include a method for measuring the gas concentration by using a gas concentration measuring device of ion electrode type, a method for measuring the gas concentration by measuring pH after preliminarily measured alkaline degrees are programmed, a method for measuring the gas concentration electrochemically after the pH value of a solution is adjusted by adding chemical to the solution, a method for measuring the gas concentration according to thermal conductivity of gas discharged by adding chemical to a solution, a method for measuring the gas concentration according to infrared ray absorption ratio of a solution, a method for measuring the gas concentration by detecting the pressure of gas discharged from a solution when ultrasonic wave is applied thereto (Japanese Patent Application Laid-Open No. 5-296904) and the like.
However, according to the above-described gas measuring method, since its operation is very complicated and upon usage, it takes a large number of time and labor, the concentration of gas in a solution produced continuously from a dissolver cannot be measured on time.
Hereinafter, artificial carbonated spring will be described as an example of solution. Generally, the artificial carbonated spring is produced as artificial carbonated spring by dissolving carbon dioxide gas of a predetermined concentration in hot water. Because it is considered that the artificial carbonated spring has an excellent effect upon distal blood circulation trouble by its strong blood vessel expanding action, it has been widely used for cure and hot spring cure. Although carbonated spring spouted naturally is used up to now, currently, the artificial carbonated spring cure has been widely used as one internal medicine cure due to development of the excellent artificial spring production method.
From the clinical research result in the artificial carbonated spring cure, it has been made evident that the effective concentration of carbon dioxide gas usable for cure becomes max from 1,000 mg/l to about 1,400 mg/l. Additionally, it has been indicated that responsibility to the carbon dioxide gas concentration differs depending on the degree of seriousness of disease and continuation period of cure. In actual artificial carbonated spring cure, it is necessary to set an appropriate concentration of carbon dioxide gas corresponding to a patient.
Thus, if the artificial carbonated spring is used for cure, the concentration of carbon dioxide gas dissolved in a solution is an important factor. The artificial carbonated spring of a predetermined concentration produced continuously with a dissolver requests to take bath just after it is stored in a storage bath. If it takes long for measurement of the concentration of gas in the artificial carbonated spring, carbon dioxide gas in the storage bath is emitted into the atmosphere so that the concentration of gas in the artificial carbonated spring drops. If a patient takes a bath in this condition, he/she cannot take bath under a desired carbon dioxide gas concentration so that the curative effect by the artificial carbonated spring cannot be expected. Further, when necessity of measuring the gas concentration a number of times repeatedly exists, it comes that the temperature of hot water itself drops.
Particularly, if the carbon dioxide gas concentration is measured according to the ion electrode type method, it takes several minutes until a measuring result is obtained, so that the measuring result cannot be obtained in a short time because several minutes is always needed for each measurement. Further, according to the method of measuring the carbon dioxide gas concentration by measuring pH after the alkaline degree is programmed preliminarily, it is necessary to measure an alkaline degree preliminarily in each case, the alkaline degree different depending on water quality. Moreover, if other ion or salt is mixed, the alkaline degree needs to be measured again, and to obtain a response result of the pH measurement, it takes some time. Thus, the carbon dioxide gas concentration cannot be measured in line at the same time when the artificial carbonated spring is produced.
On the other hand, examples of the method for producing the artificial spring include a method of dissolving bubbles of carbon dioxide gas generated by chemical reaction in hot water (Japanese Patent Application Laid-Open No. 2-270158), a method of filling hot water in a pressure tank with carbon dioxide gas under a high pressure, a method of mixing carbon dioxide gas with hot water forcibly by an agitator called static mixer in a diffuser provided halfway of a hot water conduit (Japanese Patent Application Laid-Open No. 63-242257), a method by using a multi-layer composite hollow yarn membrane dissolver (“Carbonic Water Producing Device MRE-SPA” made by Mitsubishi Rayon Engineering Co., Ltd.), and the like.
The methods by using the static mixer or multi-layer composite hollow yarn membrane dissolver are suitable for production of a large amount of the artificial carbonated spring continuously and by passing hot water through the carbon dioxide gas dissolver repeatedly by means of the circulation path, the concentration of the carbon gas can be raised gradually up to a predetermined concentration.
In case of producing artificial carbonated spring continuously, artificial carbonated spring having a predetermined carbon dioxide gas concentration can be produced by combining the carbon dioxide gas concentration measuring means with the artificial carbonated spring manufacturing method. However, the case of producing the artificial carbonated spring continuously in line has a problem in response velocity in the method for measuring the concentration of carbonated oxide gas. Although measurement based on the ion electrode method is a general method as a method for measuring the concentration of carbon dioxide gas in water, its response velocity is slow and particularly, a solution whose carbon gas dioxide concentration is 1000 to 1400 mg/l, required for the artificial carbonated spring takes long hours for the ion electrode to be balanced. Further, because gas bubbles adhere to the ion electrode thereby disabling accurate measurement, the measurement in line and on time is difficult to achieve.
Further, if the membrane is stained gradually each time of use, carbon dioxide gas becomes hard to flow, so that a deflection occurs in the relation between a carbon dioxide gas pressure and a flow rate created first, thereby disabling a right flow control. Although it may be possible to achieve the right control if the relation between pressure and flow rate is investigated each time of use, the operation for that purpose is very troublesome.
An object of the present invention is to solve the above-described problems and more particularly to provide a device and method for manufacturing carbonated spring and carbonic water having a high concentration effectively, and a device and method for manufacturing carbonated spring and carbonic water capable of always obtaining a constant carbonic acid concentration despite changes in the membrane permeating performance. Another object of the present invention is to provide a membrane module which allows soluble gas to be dissolved into liquid effectively, a method for measuring the concentration of gas dissolved in a solution produced continuously in line and on time, and a device for manufacturing a dissolved solution having a desired gas concentration effectively.